The objective of the proposed research is to develop a glucose sensor which is capable of continuous monitoring of the glucose concentrations in blood vascular fluid of a diabetic patient. Our immediate goal is to develop a glucose sensor which will be applicable in vivo for 3 days for intensive care patients. Our long range objective is to have a glucose sensor which is implantable in a patient and serves as a monitor and feedback controller for an insulin delivery system. A fuel cell type electrochemical cell will be used as the basic measurement device. An enzyme, glucose oxidase, will be immobilized on a platinum screen by a polyacrylamide gel entrapment technique and used as the working anode in the device. The unique selectivity and catalytic properties of glucose oxidase will make the measurement of true glucose level in a biological system possible. A highly active platinum black-gold cathode will be used for the reduction of the oxygen in this fuel cell system. This will assure that the cathodic reaction does not become a rate limiting step and, consequently, affect the actual glucose measurements. In vitro testing and in vivo animal evaluation of the sensor will be performed.